The present invention relates to a device for adjustably fastening two relatively rotatable members to each other between two relative rotational positions.
A device such as mentioned above is required in various structures, paticularly in those which are related with seats for human being. For example, the head rest mounted at the top of the seat back of a seat in an automobile is generally supported from a supporting frame by way of an adjustable fastening device which allows for adjustment of inclination of the head rest in accordance with the physical features and taste of the driver or passenger who is seated in front of it.
Conventionally, the devices for adjustably fastening two relatively rotatable members to each other between two relative rotational positions, like the device for fastening the head rest to its supporting frame so that its inclination can be optionally adjusted, have generally incorporated a screw means, which is adapted to be loosened and tightened by a general or exclusive tool, or which is adapted to be manipulated by the hand of the driver or passenger. In these cases, however, the inclination adjusting operation was not very easy, paticularly for women or children, and it sometimes strained and/or hurt the hands of the operator. Further, when the fastening was dependent upon frictional engagement of two relatively movable elements, the fastening operation was not sufficient, the head rest readily yielded to the impact force applied thereto in an accident and did not effectively support the head of the driver or passenger.